The present invention relates to semiconductor devices and, more specifically, to methods of forming semiconductor devices having dielectric layers.
As semiconductor devices are moving toward higher integration density, it is desirable for a capacitor of a DRAM device to have higher capacitance per unit area. A variety of approaches have been employed to increase capacitance. The approaches include reducing the thickness of the dielectric layer, increasing surface areas of top and bottom electrodes, and using a dielectric layer having a high dielectric constant. However, increasing surface areas of top and bottom electrodes is physically limited, and reducing the thickness of a capacitor dielectric layer may result in increased leakage current due to tunneling. High-k dielectric layers are being developed to decrease leakage current. It may be desirable for a high-k dielectric layer of a capacitor for use in a highly integrated semiconductor device to have an equivalent oxide thickness of approximately 6 angstroms.
Zirconium oxide (ZrO2) having a tetragonal crystalline structure has been considered as a high-k dielectric layer for use in capacitors of semiconductor devices. The dielectric constant of zirconium oxide is about 40. Zirconium oxide exhibits a satisfactory leakage current characteristic under an equivalent oxide thickness of 8 angstroms but may not be suitable for use with an equivalent oxide thickness of 8 angstroms, because of increased leakage current. On the other hand, hafnium oxide (HfO2) having a tetragonal crystalline structure exhibits a similar leakage current characteristic compared to zirconium oxide, and has a dielectric constant of about 70. However, at deposition temperatures of 300 degrees centigrade or lower, monoclinic hafnium oxide is formed. Thus, it may be difficult to form tetragonal hafnium oxide.